This invention relates to an improved process for selectively removing hydrogen sulfide from gaseous streams. In another aspect this invention relates to an improved composition suitable for use in such process.
The removal of sulfur from fluid streams can be desirable or necessary for a variety of reasons. If the fluid stream is to be burned as a fuel, removal of sulfur from the fluid stream can be necessary to prevent environmental pollution. If the fluid stream is to be processed, removal of the sulfur is often necessary to prevent the poisoning of sulfur sensitive catalysts or to satisfy other process requirements.
A variety of methods are available to remove sulfur from a fluid stream if the sulfur is present as hydrogen sulfide. These methods include using alkaline regents that unselectively absorb all acid gases. Other methods include the use of selective solid absorbants such as zinc oxide and barg iron ore. However, in general, these solid absorbants are not regenerable to their original form and must be discarded when they have become completely sulfided.
U.S. Pat. No. 4,371,728 discloses a composition comprising zinc, titanium and at least one metal promoter which is an effective absorbing composition for hydrogen sulfide and which possesses the property of being regenerable to the original absorbing composition state in the presence of oxygen when fully sulfided. Further improvements have been made upon the absorption composition of U.S. Pat. No. 4,371,728 and are disclosed in U.S. Pat. No. 4,725,415 where it is disclosed that the addition of alumina, in an amount within the range of about 10 weight percent to about 55 weight percent based upon the combined weight of the zinc, titanium and alumina, to the composition provides a more effective absorbing composition.
The absorption compositions disclosed in U.S. Pat. No. 4,371,728 and 4,725,415 not only solved the earlier problems associated with the use of solid absorbent compounds, which were unregenerable to their original form once they had become sulfided, these compounds were also effective at absorbing large amounts of sulfur that may be contained in a fluid stream while minimizing the amount of sulfur slippage. The amount of sulfur absorbed and retained by an absorbent is sometimes referred to as the sulfur loading of the composition. The sulfur slippage is the amount of sulfur contained in a fluid stream that is to be treated which passes unabsorbed through a bed of the contact material. It is desirable to have an absorbent composition which minimizes the sulfur slippage while simultaneously having a large sulfur loading capacity.
I have found that an absorbing composition comprising zinc titanate, alumina, and silica promoted with a metal selected from the group consisting of phosphorus, tungsten, molybdenum, metals of Group VIII of the Periodic Table and mixtures of any two or more thereof has substantially improved absorption properties. This improved composition has greater sulfur loading capacities over those of the prior art compositions. Moreover, the novel composition provides further reductions in the amount of sulfur slippage into a treated effluent stream.
It is thus an object of this invention to provide an improved process for removing hydrogen sulfide from fluid streams. It is a further object of this invention to provide an improved removal or absorbing composition which possesses the property of being regenerable to the original absorbing composition state in the presence of oxygen when fully sulfided. A still further object of the present invention is to provide an improved regenerable absorption composition with greater sulfur loading capabilities and which minimizes the amount of sulfur slippage into a treated effluent stream.